'\" t
.TH "SD_EVENT_SOURCE_SET_RATELIMIT" "3" "" "systemd 256.7" "sd_event_source_set_ratelimit"
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.SH "NAME"
sd_event_source_set_ratelimit, sd_event_source_get_ratelimit, sd_event_source_is_ratelimited, sd_event_source_set_ratelimit_expire_callback, sd_event_source_leave_ratelimit \- Configure rate limiting on event sources
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-event\&.h>
.fi
.ft
.HP \w'int\ sd_event_source_set_ratelimit('u
.BI "int sd_event_source_set_ratelimit(sd_event_source\ *" "source" ", uint64_t\ " "interval_usec" ", unsigned\ " "burst" ");"
.HP \w'int\ sd_event_source_get_ratelimit('u
.BI "int sd_event_source_get_ratelimit(sd_event_source\ *" "source" ", uint64_t*\ " "ret_interval_usec" ", unsigned*\ " "ret_burst" ");"
.HP \w'int\ sd_event_source_is_ratelimited('u
.BI "int sd_event_source_is_ratelimited(sd_event_source\ *" "source" ");"
.HP \w'int\ sd_event_source_set_ratelimit_expire_callback('u
.BI "int sd_event_source_set_ratelimit_expire_callback(sd_event_source\ *" "source" ", sd_event_handler_t" "callback" ");"
.HP \w'int\ sd_event_source_leave_ratelimit('u
.BI "int sd_event_source_leave_ratelimit(sd_event_source\ *" "source" ");"
.SH "DESCRIPTION"
.PP
\fBsd_event_source_set_ratelimit()\fR
may be used to enforce rate limiting on an event source\&. When used an event source will be temporarily turned off when it fires more often then a specified burst number within a specified time interval\&. This is useful as simple mechanism to avoid event source starvation if high priority event sources fire very frequently\&.
.PP
Pass the event source to operate on as first argument, a time interval in microseconds as second argument and a maximum dispatch limit ("burst") as third parameter\&. Whenever the event source is dispatched more often than the specified burst within the specified interval it is placed in a mode similar to being disabled with
\fBsd_event_source_set_enabled\fR(3)
and the
\fBSD_EVENT_OFF\fR
parameter\&. However it is disabled only temporarily \(en once the specified interval is over regular operation resumes\&. It is again disabled temporarily once the specified rate limiting is hit the next time\&. If either the interval or the burst value are specified as zero, rate limiting is turned off\&. By default event sources do not have rate limiting enabled\&. Note that rate limiting and disabling via
\fBsd_event_source_set_enabled()\fR
are independent of each other, and an event source will only effect event loop wake\-ups and is dispatched while it both is enabled and rate limiting is not in effect\&.
.PP
\fBsd_event_source_get_ratelimit()\fR
may be used to query the current rate limiting parameters set on the event source object
\fIsource\fR\&. The previously set interval and burst vales are returned in the second and third argument\&.
.PP
\fBsd_event_source_is_ratelimited()\fR
may be used to query whether the event source is currently affected by rate limiting, i\&.e\&. it has recently hit the rate limit and is currently temporarily disabled due to that\&.
.PP
\fBsd_event_source_set_ratelimit_expire_callback()\fR
may be used to set a callback function that is invoked every time the event source leaves rate limited state\&. Note that function is called in the same event loop iteration in which state transition occurred\&.
.PP
\fBsd_event_source_leave_ratelimit()\fR
may be used to immediately reenable an event source that was temporarily disabled due to rate limiting\&. This will reset the ratelimit counters for the current time interval\&.
.PP
Rate limiting is currently implemented for I/O, timer, signal, defer and inotify event sources\&.
.SH "RETURN VALUE"
.PP
On success,
\fBsd_event_source_set_ratelimit()\fR,
\fBsd_event_source_set_ratelimit_expire_callback\fR
and
\fBsd_event_source_get_ratelimit()\fR
return a non\-negative integer\&. On failure, they return a negative errno\-style error code\&.
\fBsd_event_source_is_ratelimited()\fR
returns zero if rate limiting is currently not in effect and greater than zero if it is in effect; it returns a negative errno\-style error code on failure\&.
\fBsd_event_source_leave_ratelimit()\fR
returns zero if rate limiting wasn\*(Aqt in effect on the specified event source, and positive if it was and rate limiting is now turned off again; it returns a negative errno\-style error code on failure\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
\fIsource\fR
is not a valid pointer to an
sd_event_source
object\&.
.sp
Added in version 248\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The event loop has been created in a different process, library or module instance\&.
.sp
Added in version 248\&.
.RE
.PP
\fB\-EDOM\fR
.RS 4
It was attempted to use the rate limiting feature on an event source type that does not support rate limiting\&.
.sp
Added in version 248\&.
.RE
.PP
\fB\-ENOEXEC\fR
.RS 4
\fBsd_event_source_get_ratelimit()\fR
was called on an event source that doesn\*(Aqt have rate limiting configured\&.
.sp
Added in version 248\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_event_source_set_ratelimit()\fR,
\fBsd_event_source_get_ratelimit()\fR, and
\fBsd_event_source_is_ratelimited()\fR
were added in version 248\&.
.PP
\fBsd_event_source_set_ratelimit_expire_callback()\fR
was added in version 250\&.
.PP
\fBsd_event_source_leave_ratelimit()\fR
was added in version 254\&.
.SH "SEE ALSO"
.PP
\fBsd-event\fR(3), \fBsd_event_add_io\fR(3), \fBsd_event_add_time\fR(3), \fBsd_event_add_signal\fR(3), \fBsd_event_add_inotify\fR(3), \fBsd_event_add_defer\fR(3), \fBsd_event_source_set_enabled\fR(3)
